Decadal variation in CO 2 fluxes and its budget in a wheat and maize rotation cropland over the North China Plain

[摘要] Carbon sequestration in agroecosystems has great potential to mitigate global greenhouse gas emissions. To assess the decadal trend of CO 2 fluxes of an irrigated wheat–maize rotation cropland over the North China Plain, the net ecosystem exchange (NEE) with the atmosphere was measured by using an eddy covariance system from 2005 to 2016. To evaluate the detailed CO 2 budget components of this representative cropland, a comprehensive experiment was conducted in the full 2010–2011 wheat–maize rotation cycle by combining the eddy covariance NEE measurements, plant carbon storage samples, and a soil respiration experiment that differentiated between heterotrophic and below-ground autotrophic respirations. Over the past decade (from 2005 to 2016), the cropland exhibited a statistically nonsignificant decreasing carbon sequestration capacity; the average of total NEE, gross primary productivity (GPP), and ecosystem respiration (ER), respectively, were −364 , 1174, and 810 gC m −2 for wheat and −136 , 1008, and 872 gC m −2 for maize. The multiple regression revealed that air temperature and groundwater depth showed pronounced correlations with the CO 2 fluxes for wheat. However, in the maize season, incoming shortwave radiation and groundwater depth showed pronounced correlations with CO 2 fluxes. For the full 2010–2011 agricultural cycle, the CO 2 fluxes for wheat and maize were as follows: for NEE they were −438 and −239  gC m −2 , for GPP 1078 and 780 gC m −2 , for ER 640 and 541 gC m −2 , for soil heterotrophic respiration 377 and 292 gC m −2 , for below-ground autotrophic respiration 136 and 115 gC m −2 , and for above-ground autotrophic respiration 128 and 133 gC m −2 . The net biome productivity was 59 gC m −2 for wheat and 5 gC m −2 for maize, indicating that wheat was a weak CO 2 sink and maize was close to CO 2 neutral to the atmosphere for this agricultural cycle. However, when considering the total CO 2 loss in the fallow period, the net biome productivity was −40  gC m −2  yr −1 for the full 2010–2011 cycle, implying that the cropland was a weak CO 2 source. The investigations of this study showed that taking cropland as a climate change mitigation tool is challenging and that further studies are required for the CO 2 sequestration potential of croplands.

[学科分类] 大气科学